This is a study on the myocardial sarcolemma. Its approach is to analyze the ultrastructure of 1) the glycocalyx with electron microscope cytochemical techniques and 2) the bilayer with freeze-fracture techniques. The specific aims are to determine 1) if the glycocalyx and th intramembrane particles (IMP's) seen in freeze-fractured membranes are related to membrane permeability and 2) how these components of themembrane ar related to each other. The methodology is to examine their morphology after perturbations which alter membrane permeability and during maturation of the sarcolemma. Structural changes in the bilayer (especially IMP's) and the cell surface will be related to the onset, to the degree and to the prevention of altered membrane function. To this end the following perturbations will be used in the perfused rabbit septum:" 1) Ca depletion and repletion, 2) ischemia and anoxia and 3) drug interventions, i.e. verapamil, digitalis, anesthetics. The developmetal studies will compare the structure of the sarcolemmal components in the neonate and adult rat heart. Investigation of the relationship between the glycocalyx and IMP's will involve capping components of the cell surface (sialic acid, Con A) and monitoring the fractured sarcolemma for parallel distribution of the iMP particles. In reverse, clustering of the IMP's will be induced and the cell surface distribution of cytochemical markers noted. Conventional freeze-fracture techniques plus refinements such as ultra-rapid freezing, rotary shadowing will be used to describe and quantify IMP"S (number, distribution, size, substructure). Thin-section microscopy will use colloidal iron hydroxide, cationized ferritin, Con A and tannic acid fixation. The proposed research has a two-fold significance: 1) By testing whether the glycocalyx and IMP's are related to permeability of the membrane it addresses a question fundamental to the biology of all cells and 2) it focuses on the structure-function relationships (physiologicala nd pathophysiological) of the "greater membrane," where in the heart there is little information, using state of the art techniques.